1. Field of the Invention
The present invention relates in general to an apparatus for shifting a two-speed axle for a vehicle and in particular to a control apparatus for an electric motor actuated shifting apparatus.
2. Description of the Prior Art
In truck-type vehicles where heavy loads are being hauled, it is advantageous to have available a plurality of gear ratios between the engine and the drive wheels for quickly and efficiently bringing the vehicle up to speed and maintaining a desired engine speed at various road speeds. One method of obtaining a relatively large number of gear ratios is to utilize a multi-speed transmission with a multi-speed drive axle. For example, a four-speed transmission and a two-speed axle combination provides eight gear ratios.
In prior art two-speed axle controls, an electric motor is utilized to actuate the shifting mechanism. The motor is bi-directional and, therefore, is actuated in one direction to shift into low speed and is actuated in the other direction to shift into high speed. The motor control circuit utilizes limit switches to sense when the motor reaches the fully shifted position and breaks the power circuit to the motor. Such switches are subject to power surges and arcing. If the switch fails in the closed mode, the motor will continue to operate until the switch is broken or the motor burns up.